1. Field of the Invention
The subject invention pertains to polyether polyols suitable for the preparation of polyurethane foams. More particularly, the subject invention pertains to polyether polyols initiated with melamine and coinitiated with toluene diamine which have lower viscosity than their all-toluene diamine initiated analogues.
2. Description of the Related Art
Melamine is an inexpensive readily available raw material which is finding increased usefulness in the preparation of flame-retardant polyurethane foams. See, for example, U.S. Pat. Nos. 4,745,133, 4,258,141, 4,849,959, 4,826,884, and 4,892,893.
Unfortunately, it is difficult to form dispersions of melamine in polyether polyols generally used to form polyurethane because the relatively coarse particle sizes commercially available tend to settle out over time. Thus continuous agitation or mixing melamine with polyol just prior to use is generally necessary.
To overcome these deficiencies, grinding of melamine in situ in the polyol at high local energy densities has been proposed. Further stability of the dispersion thus prepared is achieved through addition of special surfactants. See, for example, U.S. Pat. No. 4,293,657. However, in situ crushing of the polyol is time consuming and expensive. Moreover, the fine dispersions have large particle surface area, resulting in dispersions of high viscosity. The specialized surfactants add to the cost and may affect the properties of polyurethanes prepared therefrom. Finally, the melamine, whether coarse or fine, is largely unreacted with the isocyanate components, and therefore acts as an inert filler in the foam, generally detracting from the foam physical properties.
Polyether polyols based on melamine have been proposed, see for example U.S. Pat. Nos. 4,656,201 and 3,812,122. However, the products of these processes are not wholly satisfactory, and their preparation difficult.
Polyether polyols initiated with toluene diamine and their use in polyurethane foams is well known. However, the polyols initiated with toluene diamine are of relatively high viscosity, thus limiting their use. Toluene diamine initiated polyols may also improve the flame retardance of polyurethane foams prepared therefrom. Addition of melamine to such polyols would be expected to further increase polyurethane foam flame retardancy, but again continuous agitation is required for coarse melamine, while crushed melamine would increase the viscosity still further to totally unacceptable limits.
It would be desirable to produce polyols containing melamine in such a form that stable polyols are obtained at reasonable cost, and in which the melamine serves as more than merely a flame retardant filler. It would be desirable also to prepare toluene diamine polyols having lower viscosity than existing products.